This invention relates to a dual containment pipe system for installation within an existing conduit, and more particularly to a dual containment pipe system with two verifiably non-leaking barrier/pipes that are separated uniformly with a minimum annular space while maximizing the cross-sectional area of the primary pipe used to transport the effluent. The newly created annular space is suitable for a leak detection system.
There is continuing need to provide pipes and methods of installation for rehabilitating existing pipelines. Due to the fact that many existing conduits handle hazardous liquids, chemicals and petroleum products, and that such pipelines are often located underground, it is desirable to install leak detection systems to meet new environmental regulations and assure health and safety of present and future generations. In these situations it is preferable to be able to rehabilitate and retrofit existing conduits without having to excavate.
One such two-wall leakage detection system for an existing conduit is disclosed in U.S. Pat. Nos. 5,172,730 and 5,305,798, which issued on Dec. 22, 1992 and Apr. 26, 1994, respectively, and is assigned to the assignee herein, the contents of which are incorporated herein by reference. While this existing two-wall pipe and leakage detection system is satisfactory, it utilizes a soft absorbent or felt-type material to form the annular space. It is advantageous in that it is suitable for retrofitting relatively long lengths of existing pipe.
An alternative construction of a pipeline monitoring leak containment system is illustrated in U.S. Pat. No. 5,072,622 issued on Dec. 17, 1991 to Roach et al. The pipe system disclosed by Roach et al. includes a pipe having an exterior wall in tight engagement with the interior wall of the carrier pipe with at least one groove located in the exterior surface of the containment pipe. The groove and the interior wall of the outer carrier pipe define at least one passageway. While it is believed that this system is suitable for relatively short lengths, it is limiting in that the containment pipe need be of the substantially rigid type and tends to be expensive to form such grooves on a wide variety of pipes of different sizes. An advantage of this system is that the space formed in the groove should remain uniform along the length of the groove.
It has been suggested to provide a dual containment system utilizing two separate components of liners and a drainage net therebetween. This system allows the existing conduit to function as the secondary containment pipe, if sound. The drainage net provides longitudinal and circumferential channels for directing any liquid leaks to the six o'clock position where a leak detection cable can be located. This system is considered acceptable for many installations, but does require installation of three elements when the existing conduit needs repair.
A well-known process for rehabilitation of existing conduits generally utilizing a flexible liner to be cured in place is the "Insituform.RTM." method described in U.S. Pat. Nos. 4,009,063 and 4,064,211, the contents of which are incorporated herein by reference. Other flexible rehabilitation systems include Paltem.RTM. as described in U.S. Pat. Nos. 4,334,943 and 4,600,615. Another rehabilitation process known as the "NuPipe.RTM." process described in U.S. Pat. Nos. 4,867,921 and 5,255,624, the contents of which are incorporated here by reference. In this latter process a substantially rigid replacement pipe is installed in a flattened and folded shape, heated and expanded to the shape of the original conduit. A further rehabilitation system is diameter reduction as described in U.S. Pat. Nos. 4,923,663 and 5,340,524 and Canadian Patent No. 1,241,262.
In the Insituform.RTM. Process, a lining tube may be pulled in or inverted into the existing conduit. When it is everted, the lining tube is provided on its outer side with an impermeable coating or film which after eversion becomes the inner surface of the pipeline providing a smooth flow enhancing surface to the interior of the relined pipeline or passageway. While the Insituform.RTM. process is extremely viable for relining long lengths of existing conduits, it would not be suitable to provide grooves on the outer surface of such a liner if a dual containment configuration were desired. A separate body of absorbent material may be provided as in U.S. Pat. No. 5,172,730, identified above.
Accordingly, it is desirable to provide an improved dual containment pipe system which overcomes the short-coming of the prior art identified.